The present invention relates to a device and a method for the detection of composite defects, particularly a detection of composite defects by means of ultrasound. In particular, the present invention relates to the detection of composite defects between non-metallic materials by means of ultrasound.
Composite materials are used in a very wide range of technical fields. A composite material is a material made up of two or more materials joined to one another, wherein the composite material has different material properties than its individual components. The material properties and geometry of the components and also the quality of the bond between these components are of importance for the properties of the composite materials. So, composite defects can for example lead to detachments, crack formation, poor heat conduction properties, etc. In particular, material composites of this type are to be found in the building industry. There, composite defects can for example cause a detachment of carbon fibre reinforcements such as slats and rods in slots or webs or also of plaster from a non-metallic substrate, such as for example concrete or brickwork. Particularly in the case of load bearing elements, detachments of this type can be relevant from a technical safety viewpoint.
For example, the planning of rail corridors, as well as the introduction of uniform load factors for the use of trains with axle loads of up to 30 t requires the reinforcement of numerous railway bridges in almost all European countries. Internationally, carbon-fibre reinforced plastics (CFRPs) are being used increasingly for reinforcing concrete bridges.
Only a perfect bond between the CFRP reinforcement, either realised as a slat or applied as a near-surface reinforcement in slots, guarantees maximum reinforcement effect. Some persons responsible for railway infrastructure distrust this new method of CFRP reinforcement and almost never make use of it. In order to increase trust in the new method amongst infrastructure owners and to allow the executing company the proof that the service provided by them fulfils the requirements, it is necessary to be able to clearly prove a satisfactory quality of execution of the reinforcement.
Known testing methods for the detection of detachments as well as composite defects comprise the impact echo method (tap test) by means of a manually guided wheel for example, which method is for example used in aircraft construction for detecting composite defects. A further method for the detection of composite defects is acoustic emission analysis. Particularly in the building industry, the composite has hitherto either not at all been investigated or been investigated with active infrared thermography. In the case of the hitherto favoured method of active thermography, the composite is heated and subsequently the surface temperatures on a cross sectional area of approx. 50×50 cm during a cooling time of approx. 5 min are recorded. Expensive equipment is required for the carrying out of a thermographic investigation, such as for example a thermal camera with good thermal and geometric resolution. Furthermore, during the heating, the surface of the composite material must constantly be monitored, as temperatures which are too high can possibly damage the structure of the for example epoxy-resin-bonded reinforcements. In addition, the thermography method is very tedious on account of the long cooling times. In summary, it is to be determined that in addition to the energy-intensive heating of the surfaces to be investigated, the tedious carrying out of the test and the insufficient precision during the investigation of detachments at CFRP rods in slots are definitely disadvantageous.
Furthermore, testing methods by means of ultrasound are known for composite materials. For example, the use of dry coupling ultrasound sensors for crack detection in multilayer aluminium structures is known from aircraft construction. In this case, the dry electromagnetic sending and receiving, the so-called EMUS method is used. In this case, an ultrasound wave is excited in the uppermost layer in accordance with the principle of EMUS conversion. This method cannot however be used in the case of the non-metallic materials typically used in the building industry. Frequency ranges around 100 MHz are typically used for the EMUS method. Further ultrasound testing methods make use of the acoustic impedance of the material to be tested. A comparison test specimen is however required for the characterisation of the results of such impedance-dependent methods.
With reference to that stated above, the present invention suggests a method as well as a device as recited in the independent claims. Further advantageous configurations, details, aspects and features of the present invention are apparent from the dependent claims, the description as well as the attached drawings.